Coal occurs in horizontal beds which in the case of bituminous coal are frequently of great extent. The beds vary in thickness from a foot or two to one hundred feet or more, and occur at varying depths. There are two principal methods for mining coal. Firstly, there is strip mining. In this method, the top soil is removed and the underlying coal deposit is collected. Strip mining generally causes severe environmental degradation in that the top soil is removed and covered, the surface and under-surface drainage of the land is seriously disturbed and strongly acidic compounds are commonly leached out of the material exposed after the overburden and coal are removed. Restoration of the land after strip mining is expensive and is seldom successful. Thus, strip mining is increasingly regarded as unacceptable because of the associated destruction of the environment.
The second method for collecting coal involves deep coal mining. Deep mining causes severe ecological degradation, principally due to the amount of rock brought up to the surface with the coal, and coal dust or other fumes. Such mining is costly, and requires a large amount of manual labour. Inevitably also, deep coal mining is accompanied by a high incidence of accidents, caused by rock falls and gas explosions. In addition, the coal dust in the mine atmosphere causes lung problems and it is well known that many coal miners are afflicted by a blacklung disease. Lastly, in deep mining only about half of the coal in a seam is extracted. In fact, most of the coal is not mined at all because the seams are either too thin or too deep to permit economic working.
The method described herein avoids all the foregoing disadvantages of conventional coal mining techniques.